1. Field of the Invention
This invention relates to a carburetor for an internal combustion engine that generates air-fuel mixture for the internal combustion engine, and is particularly applicable to the internal combustion engine for an automobile, a motorcycle, a scooter, a snowmobile, a personal watercraft, etc.
2. Description of the Related Art
FIG. 42 shows structure of main parts of conventional carburetors for internal combustion engines. FIG. 42 is an explanatory drawing showing a structure in which a venturi portion is disposed upstream of a throttle valve.
In FIG. 42, a carburetor 1 of an internal combustion engine has a venturi portion 2. The venturi portion 2 is structured so as to squeeze an air breathed in the carburetor 1 and to increase a speed of the air. A fuel 5 of a liquid state is supplied to the carburetor 1. A fuel discharge nozzle 3 vaporizes the fuel 5 while the air 6 is breathed in the carburetor 1 so that the fuel is vaporized and discharged from the nozzle 3. Thus, a vaporized air-fuel mixture 8 of the fuel 7 and the air 6 is supplied.
In the fuel discharge nozzle 3 of the carburetor 1, the liquid fuel 5 is drawn out by the air accelerated at the venturi portion 2 due to a negative pressure generated by a piston action of the internal combustion engine. Then, the fuel is discharged from a leading end of the nozzle 3 as a vaporized fuel 7 in the form of a fine mist. A throttle valve 4 is disposed upstream or downstream of the venturi portion 2. The throttle valve 4 regulates a flow rate of the air 6 so as to control an output of the internal combustion engine.
That is, the air 6 induced into the carburetor 1 increases the flow velocity at the venturi portion 2 so as to atom the liquid fuel 5 from the fuel discharge nozzle 3. Consequently, the mist fuel 7 is mixed with the air 6 and discharged toward a downstream side of the venturi portion 2 in the form of air-fuel mixture 8.
As a result, if an opening of the throttle valve 4 is smaller, the velocity of the air flowing the venturi portion 2 becomes lower. Then, the fuel 7 discharged from the nozzle 3 becomes hard to be atomized, thereby possibly deteriorating an output and a fuel consumption of the internal combustion engine as well as an exhaust gas emission. Thus, it is important to atomize the fuel in order to improve the output and the fuel consumption of the internal combustion engine as well as the exhaust gas emission.
As a conventional art improving atomization of a discharged fuel of a fuel supplying device for an internal combustion engine, there are various techniques proposed. One example heats and vaporizes the fuel by a hot water or a PTC heater or the like. Another example atomizes the fuel by a pressurized air. Still another example atomizes the fuel by an ultrasonic vibration.
Among them, Japanese Laid Open Patent Publication No. 5-118252 and No. 10-196458 are known as conventional arts related to an improvement of atomization of a fuel in a carburetor system except a fuel injection system. No. 5-118252 shows a carburetor and No. 10-196458 shows a heating device for a carburetor.
In the Publication No. 5-118252, a straightening plate is provided from a position of a throttle valve of a manifold part toward a mixture discharge opening The plate serves to partition the manifold part into a needle valve hole side and a throttle valve hole side in a diameter direction. It prevents an air-fuel mixture from becoming turbulent, increases a fuel density of the mixture and provides a fixed flow of the mixture. However, this system cannot facilitate atomization sufficiently.
In the Publication No. 10-196458, the heating device for the carburetor has a hot water supplying conduit for supplying hot water to the carburetor and a hot water discharging conduit for discharging the hot water after heating the carburetor. The conduits are connected to the carburetor by a joint. A water receiving part is provided on an outer wall part diagonally ahead or diagonally behind a carburetor main body so as to correspond with an end position of a throttle valve in an approximately idling opened timing while making an opening direction approximately parallel to a valve shaft of the throttle valve. A carburetor side connecting port of the joint is liquid tightly inserted into an opening part of the water receiving part. Either the hot water supplying conduit or the hot water discharging conduit is connected to respective two piping side connecting ports of the joint A partitioning member is provided on the carburetor side connecting port of the joint. The partitioning member sections the inside of the carburetor side connecting port into a chamber communicated with the hot water supplying conduit and a chamber communicated with the hot water discharging conduit.
However, according to the above system, new and expensive parts need be added for better atomization of the fuel so as to improve the output and the fuel consumption of the internal combustion engine as well as the exhaust gas emission. Moreover, the structure becomes complicated. Thus, it has disadvantages in terms of costs. On the other hand, a variety of improvements are proposed for the fuel injection device of the internal combustion engine. However, such improvements could not be adopted in the carburetor that is generally cheaper than the fuel injection device.
As described above, it has been difficult to improve atomization of the fuel with a simple structure and improve maximum output and fuel consumption as well as exhaust gas emission in the internal combustion engine.
In the carburetor 1 for the internal combustion engine, there have been proposed various techniques for better atomization of the fuel in order to improve the output and fuel consumption and the exhaust gas emission in the internal combustion engine. However, the aforementioned carburetor 1 cannot atomize the fuel sufficiently or needs additionally the expensive parts to improve the atomization.
On the other hand, in each of opening angles of the throttle valve 4, the air generated from the leading end of the throttle valve 4 is accelerated. When the accelerated air impinges on the leading end of the fuel discharge nozzle at the venturi portion 2, the fuel becomes atomized. However, a position of the accelerated air changes according to the opening angles of the throttle valve 4 in the conventional carburetor 1. Thus, there has been a problem that, if the air accelerated by the throttle valve 4 deviates from the leading end position of the fuel discharge nozzle 3, the fuel is hard to be atomized.